The invention relates to a vehicle wheel suspension of the semi-trailer type with trailing arms, which extend from a wheel carrier. A first trailing arm is oriented approximately in the longitudinal direction of the vehicle, and a second trailing arm extends approximately in the direction of an angle bisector between the longitudinal direction of the vehicle and the transverse direction of the vehicle. The ends of the trailing arms that are supported on the vehicle chassis by means of trailing arm bearings determine a substantially horizontal instantaneous axis for the wheel carrier relative to the spring jounce and rebound motions of the vehicle chassis. Owing to the suitable design of at least one of the trailing arms and the suitable elastic design of at least one of the trailing arm bearings, the wheel carrier can be slightly pivoted about a so-called toe axis, in particular in the toe-in direction, under the influence of braking forces or lateral forces when driving through a curve, on the wheel that is on the outside in a curve and is mounted on the wheel carrier.
With respect to the prior art, reference is made, in particular, to DE 32 42 930 C1 and, furthermore, to EP 0 052 153, even though the latter document does not show a semi-trailer axle, but rather an especially elastic construction of an elastic trailing arm bearing at various spring rates in directions that are approximately perpendicular to each other.
The person skilled in the art knows that simple semi-trailer type wheel suspensions, which are used preferably at the driven rear axles of motor vehicles, have an undesired oversteer tendency in that the wheel that is on the outside in a curve toes out subject to the action of lateral forces. A number of remedial measures to counteract this problem have already been proposed (cf., for example, DE 39 00 336 C2, DE 102 49 44 5A1, DE 32 42 930 C1). When braking or cornering, these strategies allow the wheel that is on the outside in a curve to be pivoted in the toe-in direction under the influence of lateral forces. Yet even those prior art strategies that do not exhibit any notable disadvantages from the viewpoint of driving dynamics have not gained acceptance. Hence, it has not been possible to achieve adequate stability, subject to reasonable engineering, with a wheel suspension according to DE 32 42 930 C1, which appears to have kinematic advantages and is deemed to be the closest prior art.
Based on this prior art, there is needed a kinematically advantageous wheel suspension that can also satisfy the additional demands of being put into large scale production, in particular for passenger vehicles.
This and other needs are met according to the invention by providing a support arm that is securely connected to the wheel carrier and extends over a defined distance next to the second trailing arm substantially parallel to the same, and is supported on this second trailing arm in the area between its wheel carrier sided end and the vehicle chassis sided end by way of a support The support is much softer in the substantially horizontal direction than in the substantially vertical direction. A suitable design of the second trailing arm and/or the support arm allows a slight pivot motion of the wheel carrier about the toe axis. To this end, there are a plethora of options for designing or developing the second trailing arm in such a way. One possibility of a suitable design for the second trailing arm and/or the support arm consists of configuring at least one of these two trailing arms in the manner of a so-called control blade arm so as to be rigid in the vertical direction and substantially in the transverse direction of the vehicle and so as to be elastically deformable in the horizontal plane in the longitudinal direction of the vehicle.
An alternative possibility that shall be explained in detail below in the form of an embodiment consists of a second trailing arm being an independent component that can, therefore, be separated from the wheel carrier. One end of the second trailing arm or component is connected in an articulated manner to the wheel carrier, in order to represent the toe axis.
Both the support arm proposed herein and the second trailing arm can be designed in a simple way so that they can permanently absorb the forces that are to be transmitted and that predominantly involve the lateral forces acting on the wheel. The same applies to the bearings or joints, by which the second trailing arm is ultimately connected to the vehicle chassis. Similarly, the wheel carrier with the first trailing arm can be easily designed so that it satisfies all of the requirements without having to pay particular attention to the desired pivot motion in the toe-in direction when designing the wheel carrier, for example, with respect to stability. In other words, the engineering object is achieved by using, instead of the past conventional simple semi-trailer, a semi-trailer that is formed from two components that can be slightly pivoted in relation to each other about the toe axis essentially in the horizontal plane. In this case the second trailing arm and the support arm, which is also integrally connected, like the first trailing arm, to the wheel carrier, extend preferably over a defined distance essentially parallel next to each other. The latter guarantees in an advantageous way optimal wheel guidance, especially under the influence of lateral forces. At the same time the second trailing arm can also be connected in one piece to the wheel carrier. However, this second trailing arm then has to exhibit adequate flexibility in order to produce the desired pivotability of the wheel carrier. As an alternative, the second tailing arm may be an independent component that is mounted in a slightly pivotable manner on the wheel carrier in the vicinity of the wheel.
Moreover, the trailing arm bearing of the first trailing arm is constructed in a manner analogous to that of the prior art mentioned above, that is, relatively rigid in a direction, which extends essentially in the longitudinal direction of the vehicle, and relatively soft in a direction that is perpendicular thereto, in order to allow a toe change of the wheel under the influence of lateral forces.
The support between the support arm and the second trailing arm is designed preferably in such a way that the wheel that is on the outside in a curve is pivoted in the toe-in direction under the influence of lateral forces and under the influence of braking forces in the straightline travel of each wheel. This feature is achieved, on the one hand, by a support, which is relatively soft in the substantially horizontal direction and exhibits a preset elasticity that is different in different directions. In contrast, this support is relatively hard or, more specifically, non-elastic in the substantially vertical direction, in order to be able to represent a precise wheel control. In any event in a design of the second trailing arm as an independent component that is, therefore, separable from the wheel carrier, this desired elastokinematic behavior is achieved in that the support between the support arm and the second trailing arm is disposed relative to the hinge point of the second trailing arm on the wheel carrier. This is done in such a way that the support arm and, thus, also the wheel carrier are pivoted in the substantially horizontal direction under both the influence of lateral forces and also under the influence of braking forces on the wheel, mounted on the wheel carrier, or slightly tilted in such a way relative to the second trailing arm that the wheel (the wheel that is on the outside in a curve when cornering) moves in the toe-in direction. In this context, this support between the support arm and the second trailing arm can be configured in the form of a pendulum support or a rubber bearing exhibiting an elasticity that is suitably different in different directions.
Moreover, it is advisable in terms of a wheel control that is as precise as possible under all boundary conditions, for the possible pivot motion of the wheel carrier or, more specifically, the support arm relative to the second trailing arm, to be defined by a limit stop. Finally, an arrangement of the supporting spring that is provided for the vehicle chassis and that is optimal in terms of both the force and also the necessary design space is disclosed. It is self-evident that other arrangements of the supporting spring are also possible. Moreover, the latter also applies to the arrangement of a damper that is functionally connected in parallel to the supporting spring. The embodiment that is described below and that is used to explain the invention in detail shows one possibility of this arrangement.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.